Re: [Tuxmath-devel] Including libxml2-devel library

[David B. <dav...@gm...>]

Hi Vikas,

>>> I am getting error on compilation of tuxmath. How to link the library
>>> libxml2-devel with makefile.am (if I am right)?
>>
>> I believe this is (or should be) done in configure.ac, not Makefile.am .

That's correct - configure.ac is how you determine what gets checked
when you run ./configure, which is when our package checks to see if
it the needed libs are available and sets the compilation flags.

As part of getting the mingw-cross-env crossbuild working, I recently
revised tuxmath's configure.ac fairly heavily with a lot of help from
Volker, mingw-cross-env's maintainer.  Basically, the simple way to
check for a library with autoconf is with AC_CHECK_LIB.  However, that
isn't sufficient for making a completely statically-linked program
like mingw-cross-env does, because all of the secondary dependencies
must be known at compile time.  If possible, pkg-config's
PKG_CHECK_MODULES is a more reliable way to make sure all the
dependencies are correctly linked.  However, pkg-config isn't
supported for all libraries on all systems.  Thus, we now use a
two-tier approach - attempt to find the lib first with
PKG_CHECK_MODULES, then fall back to AC_CHECK_LIB if needed.

Below is how this approach is used for SDL_mixer.  We should be able
to adapt this by substituting "libxml-2.0" for "SDL_mixer", "XML" for
"SDL_MIXER", etc.

(Note: One slight problem I have had since going to this two-step
check relates to the echo statements.  Without these statements, the
output from configure is confusing because it show the PKG_CHECK_LIB
step failing, then the AC_CHECK_LIB step succeeding, without a very
clear indication that it is a fallback check.  With the echo
statements, I had to put in another set of [] brackets, which causes
autoconf to complain/fail on the first attempt (apparently from
overquoting), but it succeeds and apparently works properly if run a
second time.  If anyone has a good fix for this, I would be most
appreciative).

Regards,

David Bruce


Excerpt from tuxmath's configure.ac: -----------------------------



dnl Check for SDL_mixer:
--------------------------------------------------------

PKG_CHECK_MODULES([SDL_MIXER],
    [SDL_mixer],
    ,
    [
      [echo "SDL_MIXER not found via pkg_config, checking with AC_CHECK_LIB:"]
      AC_CHECK_LIB([SDL_mixer],
	 [Mix_OpenAudio],
         ,
         [AC_MSG_ERROR([SDL_mixer not found!
http://www.libsdl.org/projects/SDL_mixer])]
      )
      [echo "SDL_MIXER successfully located"]
    ]
)

AC_DEFINE([HAVE_LIBSDL_MIXER],[1],[Define to 1 if you have the
`SDL_mixer` library])
CFLAGS="$CFLAGS $SDL_MIXER_CFLAGS"
LIBS="$LIBS $SDL_MIXER_LIBS"